Glucocerebrosidase in man is encoded by a gene of approximately 6.5 kb. We have isolated three full length copies of this gene, one from a HaeIII-AluI fetal genomic library and two from an EcoRI adult liver library in bacteriophage Lambda charon 4A. The 15 kb human genomic DNA segment containing this gene in all three clones has been characterized by restriction mapping. The 5' halves of the clones from the two different libraries show significant size heteromorphisms. We are in the process of analyzing the 5' ends of the genes, and the flanking sequences for putative eukaryotic promoter/enhancer elements, and the intron-exon relationships. Extensive characterization of these clones is in progress by D-loop analysis, restriction pattern analysis, and nucleotide sequence. The aim of these studies is to construct a physical map of the human glucocerebrosidase gene and identify the structural and regulatory elements in order to correlate the structural features with different functional domains of the glycoprotein. An understanding of the structural organization of glucocerebrosidase gene will be of value in identifying and defining the molecular nature of the genetic defect(s) leading to Gaucher's disease, in addition to elucidating the molecular mechanism(s) that are altered by the mutations in the gene. This will ultimately lead to a better understanding of the regulation of the glucocerebrosidase gene in man.